It is well known that fluorescent lamps consume substantially less electrical power than conventional incandescent lighting while producing equivalent illumination levels. For example, some conventional fluorescent lamps may produce illumination equivalent to a 60-watt incandescent bulb on just 15 watts of power. Further, it is known that fluorescent lamps can often provide substantially longer service lives, sometimes in excess of nine thousand hours, than incandescent bulbs. Because of such advantages of fluorescent lighting, substantial efforts have been made to provide fluorescent lamp assemblies that can be substituted for incandescent bulbs in standard lighting fixtures.
Pursuant to such efforts, fluorescent lamps have been formed in various shapes and have been fitted with base connectors that are compatible with sockets for standard incandescent bulbs. Examples of such fluorescent lamps include ones that are sold under the trademarks "Refluor" and "Reflect-A-Star PL" by Lumatech Corporation of Oakland, California; those fixtures employ so-called PL fluorescent lamps that have U-shaped tubes with starters built into their bases. In some models of such lamps, replaceable starters are also provided. Further it is known in such lamps to provide external plug-in ballasts. Although these lamps usually produce satisfactory lighting levels, the arrangement of their components and their length prevents them from being completely satisfactory for lighting applications such as recessed lighting.
It is also known to fit fluorescent tubes and built-in starters into bulb-shaped housings. Such lamps are available from Mitsubishi Corporation under part number BFT 17 LE. In such lamps, the ballast components (i.e., reactance ballasts) are located in ballast compartments located at the base of the bulb compartments.
Adapters that permit fluorescent lamps to be used in sockets in substitution for incandescent bulbs are available from several sources and are described, for example, in U.S. Pat. Nos. 4,570,105 and 4,623,823. The adapters disclosed in those patents include hollow cylindrical housings, Edison-type bases, and covers enclosing the ends of the housings opposite the bases. Further according to the patents, toroidal ballasts are located within the housings to receive the stems of fluorescent lamps to enhance spacial efficiency. Other adapters and components for fluorescent lamps are available from Eastrock Technology, Inc. of Staten Island, New York.
Various other configurations of fluorescent lamps compatible with sockets with incandescent bulbs are suggested by the following U.S. Pat. Nos: 2,505,993; 3,551,736; 3,611,009; 3,815,080; 3,953,761; 4,093,893; 4,173,730; 4,270,071; 4,347,460; 4,375,607; 4,405,877 and 4,414,489.
One serious disadvantage of known designs of such fluorescent lamps, however, is that their ballast components often preclude the lamps from being completely satisfactorily employed in recessed lighting applications. (A recessed lighting application can be defined, for present purposes, as one in which an illuminating lamp, with or without a reflector, is mounted within a canister-like container having an open end through which the lamp shines.) Moreover, although some known fluorescent lamps may have appropriately compact dimensions for use in recessed lighting applications, actual usage of compact fluorescent lamps is problematical because the service lives of the lamps fall far short of expectations. In other words, fluorescent lamps in recessed lighting applications have demonstrated a tendency to fail over periods far shorter than their rated lives.
In recessed lighting applications, failures of fluorescent lamps are believed to be caused by high temperatures, sometimes exceeding 225.degree. F, which may be generated at the base of the stem of the lamp. Such temperatures can substantially exceed the maximum temperatures recommended by manufacturers, usually about 185.degree. F, and may cause early deterioration and failure of lamp starter and ballast components. For example, the adapter assemblies disclosed in U.S. Pat. Nos. 4,570,105 and 4,623,823 are not well adapted for use in recessed lighting applications because the stems of fluorescent lamps encompassed by the toroidal ballasts would often reach temperatures that would severely limit their service lives.